This invention relates to improvements in the provision of stress relieved air supported structures.
The majority of air supported structures presently in use include a membrane envelope which has been fabricated from commercial high strength industrial fabric such as is readily available in the particular area wherein the same is to be constructed, providing a low cost portable or semi-permanent enclosure which is adequately serviceable under conditions where temporary collapse would not be of serious consequence. With the growing interest in use of air supported structures of larger sizes and as relatively permanent installations, a need has developed to provide air supported structures having long term structural integrity and weather resistance. It is accordingly a primary object of the present invention to provide an air supported structure having long term structural integrity and weather resistance.
An air supported structure having structural integrity must be generally designed to withstand two primary types of loading, namely:
1. Static and uniform loading produced by inflation pressure within the air supported structure, which is generated from the input of air from blower systems usually provided for discharging air interiorally of the air supported structure about the perimeter thereof; and
2. The generally asymmetric loading produced by air flow over the exterior of the structure, and which is usually referred to as aerodynamic loading.
Of course, various other generally asymmetric load factors may be encountered, such as by snow, etc. However, in the absence of extreme loading caused by such other factors, and in connection with which it is unlikely that an air supported structure could be readily designed to resist the same, or in the location in which the same were excessive, use of an air supported structure would not likely be considered, air supported structures according to the present invention, and within the design limits herein specified with respect to the shape of the air supported structure and the design wind velocity thereof, will normally withstand such other loading factors.
Aerodynamic loading varies as the square of the exterior wind velocity and is proportionately much larger than the normal stresses due to inflation pressure alone. Further, although inflation pressure is constant and aerodynamic loading will generally be variable, the two types of loads are usually additive and almost invariably act in the same direction. When such non-uniform loading occurs, equilibrium conditions in the air supported structure can be achieved either by redistribution of load, or by distortion of the structure. It is believed quite obvious that distortion is undesirable and that redistribution of load factors is almost a necessity for maintenance of a usable air supported structure.
Loading conditions which would normally result in a compressive stress in rigid structures are resisted in an air supported structure as a relaxation of tensile loads imposed by the initial inflation pressure. Thus, a hemispherical dome shaped air supported structure is quite stable, as the pretensioning loads imposed by inflation pressure are distributed uniformly. However, in the case of a semi-cylindroidal shaped air supported structure, stresses resulting from pressure differential, hoop tension, are irregularly distributed. For instance, aerodynamic loading along a lateral section through a semi-cylindroidal air supported structure causes a distortion or change in radial shape along the entire length thereof in order to even approximately equalize tensions between opposed anchor points which is required in order to maintain the air supported structure in equilibrium.
In order to maintain the basic envelope of an air supported structure in substantially static equilibrium, I provide the same with a network of stress relieving members for carrying the resultants of aerodynamic and inflation pressure loads. Thus, the basic envelope distributes the pressure loads to the stress relieving members.
Accordingly, it is a further object of this invention to provide an air supported structure having an interconnected and/or interrelated network of stress relieving members which maintains the air supported structure in substantially static equilibrium under normal conditions of asymmetrical loading.
Moreover, the attitude, configuration, interconnection and/or interrelation of the basic envelope and the stress relieving members is critical in fabrication and design of an air supported structure of substantially static equilibrium. It is thus a further object of this invention to provide various design formulations for construction of an air supported structure having substantially static equilibrium.
Other objects and advantages of the invention will become apparent from the following detailed description, taken in connection with the accompanying drawings, and in which drawings: